The following patent documents are believed to represent the current state of the art:
Japanese Patent JP 2002108711;
U.S. Pat. Nos. 6,830,182; 6,853,093 5,998,858, 5,861,662 and 6,917,299;
Published PCT Application WO 2005/086546; and
U.S. Published Patent Application 2006/0049255.